With increased spectral crowding at lower frequencies, microwave communications have become a viable alternative and present some interesting opportunities. However, microwave communications have their own set of particularized problems that need to be resolved before extensive commercialization of microwave communications can be realized.
Microwave components are relatively massive mechanical elements that are both difficult and expensive to manufacture. The cost and complexity of microwave components can rapidly accelerate in systems requiring redundancies or multiple signal paths.
In point to point communication systems, redundant receivers are employed to enhance the reliability of the communications system despite occasional equipment failure. Typically, one receiver is active in the communication system while the other receiver is on hot standby-that is, it is actively receiving and can be switched into the communications system in the event of a failure of the active receiver.
A redundant receiver system is shown in FIG. 1. Microwave energy is received by an antenna and introduced into a T shaped waveguide to split the microwave energy into two forward paths. Each signal path must be filtered to the proper bandwidth and variably attenuated before reaching the receiver. Duplicate filters must be inserted in each signal path rather than in the common signal path because the filter is required to maintain isolation between the two receivers. Otherwise, the local oscillator signal from one receiver would feed through the power splitter into the other receiver causing unacceptably strong beat notes whose frequency would be the difference between the frequencies of the two local oscillators.
The challenge, then, was to drastically reduce the number of individual components required in a redundant system and, thereby, reduce the insertion losses associated with each component while maintaining or enhancing performance.
This invention met that challenge by providing a single device that performs forward bandwidth filtration, power splitting, output isolation, and variable attenuation in one compact apparatus.